From the viewpoint of achieving high-capacity data communication at a higher speed, there has been a trend in recent years in mobile terminals for high frequency communication toward an increase in the transmission signal power. In a mobile terminal, an increase in the signal power may result in deterioration of isolation of the duplexer. Theoretically, it is possible to improve the isolation of the duplexer by configuring a transmitting filter or receiving filter used in the duplexer to have an increased attenuation in the opposite band (the receiving band for the transmitting filter and the transmitting band for the receiving filter). In reality, however, the isolation becomes saturated at a certain level. The reason for this because not only a current that flows through the filters but also a current that flows through the duplexer via space serve as components having an influence on the isolation. In order to achieve a high level of isolation, it is desirable to study measures against the current that flows through the duplexer via space.
Examples of effective configurations in removing the influence of the current that flows through the duplexer via space, in other words, the influence of electromagnetic coupling components include increasing the physical distance between a source and a target to be coupled and placing an electromagnetic shielding structure. Patent Document 1 discloses a surface acoustic wave device in which a shield electrode is disposed between two surface acoustic wave filter patterns. Patent Document 2 discloses a surface acoustic wave device in which an input external terminal and an output external terminal are disposed apart from each other diagonally.
Patent Documents
Patent Document 1: JP 2006-60747 A
Patent Document 2: JP 2002-76829 A
In the case of the configuration disclosed in Patent Document 1, adequate improvements in the isolation may be achieved by increasing the size of the shielding member. However, an increase in the size of the shielding member may impair a downsizing of the duplexer. Further, in the case of the configuration disclosed in Patent Document 2, adequate improvements in the isolation may be achieved by increasing the distance between the input external terminal and the output external terminal. However, an increase in the distance between the terminals may impair a downsizing of the duplexer. The inventors realized that with the configurations disclosed in Patent Documents 1 and 2, it is difficult to achieve both the downsizing of the duplexer and improvements in the isolation.